Ionic liquid for desulfurization of light fuels

ABSTRACT

The ionic liquid for desulfurization of light fuels is 1-methyl-3-pentyl 1H-imidazolium periodate, having the structural formula: 
     
       
         
         
             
             
         
       
     
     The compound is prepared by mixing 1-methyl-3-pentyl 1H-imidazolium tetrafluoroborate with sodium periodate in dichloromethane and water, stirring the mixture for 24 hours, and extracting the compound from the product with dichloromethane. The ionic liquid may be used for the desulfurization of light fuels by bringing the ionic liquid into contact with the crude light petroleum oil at a temperature of about 50° C. with stirring for a period of time sufficient to oxidize the sulfur containing impurities to water soluble sulfones, washing the mixture with water to remove the ionic liquids and water soluble sulfones, and drying the desulfurized light fuel product.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the desulfurization of light fuels andpetroleum products, and particularly to ionic liquids for thedesulfurization of light fuels.

2. Description of the Related Art

The desulfurization of fuel constitutes a major target of oil refineriesdue to growing public concern of environment pollution from emissionsfrom the combustion of fuels. The sulfur compounds present in light fuelare converted to sulfur dioxides, which are considered to be a majorsource of acid rain and air pollution. To control the SO_(X) emissions,severe regulations are being imposed on oil refineries to reduce thesulfur content to an acceptably low limit.

The catalytic hydrodesulfurization method, which is typically employedin the refineries, requires both high temperature and high pressures ofhydrogen gas. Thus, this method entails high risk for personneloperating the refinery. Thus, alternative methods are being sought toavoid the use of high pressure and high temperature hydrogen gas.Oxidative desulfurization is particularly attractive, due to itsrelatively low risk and environmental impact.

Recently, ionic liquids have received considerable interest due to theirenvironmentally friendly properties, such as low volatility and thermalstability. Several methods have been developed that use hydrogenperoxide in combination with ionic liquids, and combine solventextraction with oxidation of dibenzothiophene (DBT), which is the majorsulfur compound in light oil. However, these techniques require the useof an external oxidant and presently lack efficiency for completeremoval of DBT.

Thus, an ionic liquid for desulfurization of light fuels solving theaforementioned problems is desired.

SUMMARY OF THE INVENTION

The ionic liquid for desulfurization of light fuels is 1-methyl-3-pentyl1H-imidazolium periodate, having the structural formula:

The compound is prepared by mixing 1-methyl-3-pentyl 1H-imidazoliumtetrafluoroborate with sodium periodate in dichloromethane and water,stirring the mixture for 24 hours, and extracting the compound from theproduct with dichloromethane. The ionic liquid may he used for thedesulfurization of light fuels by bringing the ionic liquid into contactwith the crude light petroleum oil at a temperature of about 50° C. withstirring for a period of time sufficient to oxidize the sulfurcontaining impurities to water soluble sulfones, washing the mixturewith water to remove the ionic liquids and water soluble sulfones, anddrying the desulfurized light fuel product.

These and other features of the present invention will become readilyapparent upon further review of the following specification anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chemical equation showing a reaction scheme for thesynthesis of 1-methyl-3-pentyl 1H-imidazolium bromide.

FIG. 2 is the H¹ NMR spectrum of 1-methyl-3-pentyl 1H-imidazoliumbromide synthesized according to the scheme of FIG. 1.

FIG. 3 is the C¹³ NMR spectrum of 1-methyl-3-pentyl 1H-imidazoliumbromide synthesized according to the scheme of FIG. 1.

FIG. 4 is the FT-IR spectrum of 1-methyl-3-pentyl 1H-imidazolium bromidesynthesized according to the scheme of FIG. 1.

FIG. 5 is a chemical equation showing the reaction scheme for thesynthesis of 1-methyl-3-pentyl 1H-imidazolium tetrafluoroborate.

FIG. 6 is the H¹ NMR spectrum of 1-methyl-3-pentyl 1H-imidazoliumtetrafluoroborate prepared according to the scheme of FIG. 5.

FIG. 7 is the C¹³ NMR spectrum of 1-methyl-3-pentyl 1H-imidazoliumtetrafluoroborate prepared according to the scheme of FIG. 5 . . . .

FIG. 8 is the FT-IR spectrum of 1-methyl-3-pentyl 1H-imidazoliumtetrafluoroborate prepared according to the scheme of FIG. 5 . . . .

FIG. 9 is a chemical equation showing the reaction scheme for thesynthesis of 1-methyl-3-pentyl 1H-imidazolium periodate, which is theionic liquid for the desulfurization of light fuels according to thepresent invention.

FIG. 10 is the H¹ NMR spectrum of 1-methyl-3-pentyl 1H-imidazoliumperiodate prepared according to the scheme of FIG. 9.

FIG. 11 is the C¹³ NMR spectrum of 1-methyl-3-pentyl 1H-imidazoliumperiodate prepared according to the scheme of FIG. 9.

FIG. 12 is the FT-IR spectrum of 1-methyl-3-pentyl 1H-imidazoliumperiodate prepared according to the scheme of FIG. 9.

FIG. 13 is a chemical equation showing the oxidation reaction of1-methyl-3-pentyl 1H-imidazolium periodate prepared according to thescheme of FIG. 9 with dibenzothiopene.

FIG. 14 is the H¹ NMR spectrum of the sulfone product of the reaction ofFIG. 13.

FIG. 15 is the C¹³ NMR spectrum of the sulfone product of the reactionof FIG. 13.

FIG. 16 is the FT-IR spectrum of the sulfone product of the reaction ofFIG. 13.

Similar reference characters denote corresponding features consistentlythroughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The ionic liquid for desulfurization of light fuels is 1-methyl-3-pentyl1H-imidazolium periodate, having the structural formula:

The circle inside the 5-member ring indicates that the ring is aromatic,i.e., it has two double bonds, and the ‘+’ sign inside the circleindicates that the ring is cationic, the charge being distributed in thering by conjugation of the double bonds. The same convention is used inthe structural formulas for 1-methyl-3-pentyl 1H-imidazolium bromide,1-methyl-3-pentyl 1H-imidazolium tetrafluoroborate, and in the drawings.The compound is prepared by mixing 1-methyl-3-pentyl 1H-imidazoliumtetrafluoroborate with sodium periodate in dichloromethane and water,stirring the mixture for 24 hours, and extracting the compound from theproduct with dichloromethane. The ionic liquid may be used for thedesulfurization of light fuels by bringing the ionic liquid into contactwith the crude light petroleum oil at a temperature of about 50° C. withstirring for a period of time sufficient to oxidize the sulfurcontaining impurities to water soluble sulfones, washing the mixturewith water to remove the ionic liquids and water soluble sulfones, anddrying the desulfurized light fuel product.

In order to investigate the usefulness of 1-methyl-3-pentylimidazolium-based ionic liquids for the desulfurization of lightpetroleum fuels, the inventors synthesized a bromide, atetrafluoroborate, and a periodate ionic liquid, tested the ability ofthe periodate compound to oxidize dibenzothiophene (which is the majorsulfur contaminant in the refining of light fuels), and performed acomparative experiment of the ability of the ionic liquids to removesulfur-containing impurities from crude petroleum light fuel samples.The experiments are reported in the following Examples.

Example 1

As shown in FIG. 1, a first 1-methyl-3-pentyl imidazolium ionic liquidis made by mixing 2.2 mmol of 1-bromopentane and 2 mmol of N-methylimidazole to form a mixture. Mixing preferably occurs for about 10seconds. This mixture is then irradiated with microwave radiation in aconventional microwave oven. The microwave radiation has a power ofabout 240 W, and the mixture is irradiated for about 30 seconds.Following irradiation, the mixture is removed from the oven, shakenwell, and then re-irradiated for another 30 seconds to form a clear,viscous, single-phase solution. The single-phase solution is thencooled, washed twice with 2 mL of ether to remove unreacted startingcomponents, and then dried under vacuum at a temperature of about 70°C., yielding about 86% pure 1-methyl-3-pentyl 1H-imidazolium bromideionic liquid having the structure:

FIGS. 2, 3 and 4 illustrate, respectively, the H¹ NMR spectrum of the1-methyl-3-pentyl 1H-imidazolium bromide ionic liquid, the C¹³ NMRspectrum of the 1-methyl-3-pentyl 1H-imidazolium bromide ionic liquid,and the FT-IR spectrum of the 1-methyl-3-pentyl ′1H-imidazolium bromideionic liquid. Spectral peaks for the H¹ NMR spectrum of FIG. 2 aresummarized as: (DMSO-d₆, 300 MHz) δ 0.81 (t, J=6.7 Hz, 3H), 1.17-1.28(m, 4H), 1.76-1.81 (m, 2H), 3.91 (s, 3H), 4.18 (t, J=7.3 Hz, 2H), 7.57(s, 1H), 7.60 (s, 1H), 9.53 (s, 1H). Spectral peaks for the C¹³ NMRspectrum of FIG. 3 are summarized as: (DMSO-d₆, 75 MHz) δ 12.1, 20.1,26.2, 27.9, 34.4, 47.6, 120.8, 122.0, 134.9. The spectral peaks for theFT-IR spectrum of FIG. 4 are summarized as: 3435, 3154, 3140, 3007,2956, 2931, 2800, 1676, 1572, 1518, 1462, 1427, 1381, 1338, 1286, 1232,1165, 1080, 852, 762, 651, 621 cm⁻¹.

Example 2

From the 1-methyl-3-pentyl 1H-imidazolium bromide ionic liquid, a second1-methyl-3-pentyl imidazolium ionic liquid is further developed, asillustrated in FIG. 5. The 1-methyl-3-pentyl 1H-imidazolium bromideionic liquid, prepared as described above, is stirred with 3 mmol ofNaBF₄ in a mixture of dichloromethane (DCM) and water having a molarratio of 7:3 for 24 hours at room temperature. The resulting secondionic liquid is extracted with DCM and dried under vacuum to provide1-methyl-3-pentyl 1H-imidazolium tetrafluoroborate ionic liquid havingthe structure:

FIGS. 6, 7 and 8 illustrate, respectively, the H¹ NMR spectrum of the1-methyl-3-pentyl 1H-imidazolium tetrafluoroborate ionic liquid, the C¹³NMR spectrum of the 1-methyl-3-pentyl 1H-imidazolium tetrafluoroborateionic liquid, and the FT-IR spectrum of the 1-methyl-3-pentyl1H-imidazolium tetrafluoroborate ionic liquid. Spectral peaks for the H¹NMR spectrum of FIG. 6 are summarized as: (CDCl₃, 300 MHz) δ 0.89 (t,J=6 Hz, 3H), 1.33 (br s, 4H), 1.85-1.92 (m, 2H), 3.93 (s, 3H), 4.17 (t,J=7.2 Hz, 2H), 7.27-7.41 (m, 2H), 8.79 (s, 1H). Spectral peaks for theC¹³ NMR spectrum of FIG. 7 are summarized as: (DMSO-d₆, 75 MHz) δ 13.5,21.7, 27.9, 29.4, 35.9, 49.7, 122.2, 123.6, 135.8. The spectral peaksfor the FT-IR spectrum of FIG. 8 are summarized as: 36221, 3421, 3160,3119, 2960, 2933, 2872, 1632, 1573, 1462, 1437, 1171, 1057, 849, 764,623 cm⁻¹.

Example 3

The 1-methyl-3-pentyl 1H-imidazolium tetrafluoroborate ionic liquidprepared as described above may be used to make a third1-methyl-3-pentyl imidazolium ionic liquid, as shown in FIG. 9. The1-methyl-3-pentyl 1H-imidazolium tetrafluoroborate ionic liquid is putin a round bottom flask and stirred with 3 mmol of NaIO₄ (sodiumperiodate) in a mixture of dichloromethane (DCM) and water having amolar ratio of 7:3 for 24 hours at room temperature. The resulting thirdionic liquid is extracted with DCM and dried under vacuum to provide a1-methyl-3-pentyl 1H-imidazolium iodate ionic liquid having thestructure:

FIGS. 10, 11 and 12 illustrate, respectively, the H¹ NMR spectrum of the1-methyl-3-pentyl 1H-imidazolium iodate ionic liquid, the C¹³ NMRspectrum of the 1-methyl-3-pentyl 1H-imidazolium iodate ionic liquid,and the FT-IR spectrum of the 1-methyl-3-pentyl 1H-imidazolium iodateionic liquid. Spectral peaks for the H¹ NMR spectrum of FIG. 10 aresummarized as: (CDCl₃, 500 MHz) δ 0.78 (t, J=6.7 Hz, 3H), 1.22 (br s,4H), 1.77-1.80 (m, 2H), 3.87 (s, 3H), 4.09 (t, J=7.2 Hz, 2H), 7.34-7.36(m, 2H), 8.71 (s, 1H). Spectral peaks for the C¹³ NMR spectrum of FIG.11 are summarized as: (CDCl₃, 125 MHz): δ 135.6, 123.69, 122.3, 49.9,36.3, 29.5, 27.9, 21.7, 13.5. The spectral peaks for the FT-IR spectrumof FIG. 12 are summarized as: 3572, 3533, 3514, 3498, 3477, 3151, 3113,3007, 2958, 2933, 2864, 1629, 1573, 1462, 1381, 1232, 1168, 1062 cm⁻¹.

Example 4

In order to test the efficacy of the ionic liquids at desulfurization oflight fuels, a solution of dibenzothiophene in petroleum ether (0.25 mgin a 2 mL solution) was placed in a round bottom flask. The1-methyl-3-pentyl 1H-imidazolium periodate ionic liquid, prepared asdescribed above, was added to the mixture and stirred vigorously forabout 6 hours at a temperature of about 50° C. in open atmosphere. Thereaction was monitored by thin layer chromatography (TLC). After thereaction was over, the reaction mixture was washed four times in 5 mL ofwater. The unreacted ionic liquid and sulfone of dibenzothiophene werewashed out with the water. The resultant petroleum ether was dried andcollected in a round bottom flask. The reaction is illustrated in FIG.13, where the 1-methyl-3-pentyl 1H-imidazolium periodate ionic liquid isrepresented as [pmlm]IO₄.

FIGS. 14, 15 and 16 illustrate, respectively, the H¹ NMR spectrum of theisolated sulfone, the C¹³ NMR spectrum of the isolated sulfone, and theFT-IR spectrum of the isolated sulfone. Spectral peaks for the H¹ NMRspectrum of FIG. 14 are summarized as: (CDCl₃, 500 MHz) δ 7.54 (t, J=7.5Hz, 2H); 7.65 (t, J=7.5 Hz, 2H); 7.80-7.84 (m, 4H). Spectral peaks forthe C¹³ NMR spectrum of FIG. 15 are summarized as: (CDCl₃, 125 MHz): δ138.0, 134.0, 131.8, 130.5, 122.3, 121.7, 77.4, 77.2, 76.9. The spectralpeaks for the FT-IR spectrum of FIG. 16 are summarized as: 3421, 3082,2958, 1817, 1591, 1575, 1479, 1452, 1435, 1288, 1165, 1157, 1118, 1074,1047, 943, 869, 756, 734, 711, 613, 580, 567, 538 cm⁻¹.

Example 5

Crude petroleum includes dibenzothiophene, benzothiophene and thiopheneas major sulfur-containing materials. Thus, removal of these thiophenesis an important step towards desulfurization of fuel oils. Tostandardize the reaction conditions for oxidation, the three ionicliquids described above were each tested as oxidizing agents. Theresults are summarized in the Table 1 below. In Table 1, the1-methyl-3-pentyl 1H-imidazolium bromide ionic liquid is represented as[pmIm]Br, the 1-methyl-3-pentyl 1-H-imidazolium tetrafluoroborate ionicliquid is represented as [pmlm]BF₄, and the 1-methyl-3-pentyl1H-imidazolium periodate ionic liquid is represented as [pmIm]IO₄. Thefirst two ionic liquids, prepared as described above, are found to benot effective enough for oxidation of dibenzothiophene. The1-methyl-3-pentyl 1H-imidazolium periodate was found to furnish the bestresults in terms of conversion and yield when the reaction was carriedout at 50° C. for 6 hours. In Table 1 below, room temperature isabbreviated as RT.

TABLE 1 Comparative Results for Oxidation of Thiophenes by Ionic LiquidsIonic Liquid Time (hours) Temperature (° C.) Yield (%) [pmIm]Br 5 RT —[pmIm]BF₄ 6 RT — [pmIm]IO₄ 5 RT 21 [pmIm]IO₄ 3 50 46 [pmIm]IO₄ 6 50 98

The fuel sample was found almost completely DBT free and thecorresponding sulfone of DBT was isolated from the aqueous part bysolvent extraction and characterized by NMR spectroscopy. The1-methyl-3-pentyl 1H-imidazolium periodate ionic liquid was effective inremoving all three organosulfur compounds. The 1-methyl-3-pentyl1H-imidazolium periodate ionic liquid contains the active oxidizingspecies periodate, whereas the other two ionic liquids do not bear sucha moiety, which explains why the 1-methyl-3-pentyl 1H-imidazoliumperiodate ionic liquid is an oxidizing agent and the other two are not.The thiophene and benzothiophenes are removed nearly quantitatively(>95%), as indicated by thin layer chromatography (TLC). However, 81%and 93% are isolated yields of the corresponding sulfones. Typically,the isolated yields are lower than actual conversion yields due to someloss of product during the process.

The percent yield of isolated sulfone is calculated using the mass ofsulfone. The mass of sulfones were divided by the molar mass of sulfoneto yield the number of moles of sulfone. The moles of sulfone are theactual yield. The moles of benzothiophenes are known, which is thetheoretical yield. The percent yield of any reaction is calculated usingmoles of reactants and moles of products is:

${{Percent}\mspace{14mu} {Yield}} = {\frac{{moles}\mspace{14mu} {of}\mspace{14mu} {actual}\mspace{14mu} {yield}}{{moles}\mspace{14mu} {of}\mspace{14mu} {theoretical}\mspace{14mu} {yield}} \times 100.}$

By substituting the number of moles of sulfones isolated and the molesof benzothiophenes, the percent of sulfur isolated from the modelgasoline may be calculated in the form of sulfones as:

${{Percent}\mspace{14mu} {Sulfur}\mspace{14mu} {Isolated}} = {\frac{{moles}\mspace{14mu} {of}\mspace{14mu} {sulfones}\mspace{14mu} {isolated}}{{moles}\mspace{14mu} {of}\mspace{14mu} {benzothiophenes}\mspace{14mu} {used}} \times 100.}$

The 1-methyl-3-pentyl 1H-imidazolium periodate ionic liquid is found tobe effective at removing about 90% of the sulfur from the modelgasoline.

It is to be understood that the present invention is not limited to theembodiments described above, but encompasses any and all embodimentswithin the scope of the following claims.

We claim:
 1. An ionic liquid for desulfurization of light fuels,comprising 1-methyl-3-pentyl 1H-imidazolium periodate, having thestructural formula:


2. A method of desulfurizing light fuels, comprising the steps of:bringing the ionic liquid into contact with crude light petroleum oil ata temperature of about 50° C. with stirring for a period of timesufficient to oxidize any sulfur-containing impurities in the crudelight petroleum oil to water soluble sulfones; washing the mixture withwater to remove the ionic liquids and water soluble sulfones; and dryingthe desulfurized light petroleum oil product.
 3. The method ofdesulfurizing light fuels according to claim 2, wherein said period oftime sufficient to oxidize any sulfur-containing impurities comprisesabout six hours.
 4. A method of making 1-methyl-3-pentyl 1H-imidazoliumperiodate, comprising the steps of: mixing 1-methyl-3-pentyl1H-imidazolium tetrafluoroborate with sodium periodate indichloromethane and water; stirring the mixture for 24 hours; andextracting the 1-methyl-3-pentyl 1H-imidazolium periodate from themixture with dichloromethane.